In general, a brake is known to serve to convert kinetic energy of a running vehicle into thermal energy by mechanical friction of a friction material and dissipate the converted thermal energy in the air and decelerate or stop the vehicle.
In a driving scheme of generating mechanical friction, a hydraulic caliper including a hydraulic cylinder and a piston is largely used in vehicles, and here, force applied to step on a brake pedal by a driver is amplified by a hydraulic booster, and the amplified hydraulic pressure is delivered to a hydraulic caliper (having a large sectional area) installed in each wheel through a master cylinder (having a small sectional area) and an oil pipe.
Consequently, force equivalent to the product of hydraulic pressure delivered to a slave cylinder of the caliper and the sectional area of the caliper cylinder pushes the piston, and the piston moves pads toward a disk to make the pads brought into contact with the disk, and subsequently generates great clamping force.
Eventually, force equivalent to the product of the clamping force and a coefficient of friction of a contact surface of the disk exerts as braking force on the disk, and resultantly, small pedal force is converted into great clamping force so as to be used to perform braking.
Types of hydraulic disk brake systems are classified as a floating type disk brake system, a fixed caliper type disk brake system, and a floating caliper type disk brake system.
Thereamong, the floating caliper type disk brake system is commonly used.
The floating caliper type brake system has a structure in which a hydraulic piston pressing unit moves one inner pad to a disk and make the pad clamped to the disk and a caliper housing slides in the opposite direction of the movement of the inner pad by reaction force since then to pull an outer pad toward the disk to clamp both sides of the rotary disk to brake the disk.
Since the floating caliper type brake system has a small number of components, is light in weight, and has an excellent cooling operation, the floating caliper type brake system is used in most automobiles. However, at an initial braking stage, since the inner pad is first clamped all the time and the outer pad is subsequently operated upon receiving the reaction force, wear variations may be generated.
Also, until before the outer pad is clamped, braking force at the initial braking operation is inadequate.
In line with an alteration to hybrid, fuel cell, electric vehicles as future automobiles and demand for vehicle safety and environment-friendliness, the necessity for electro-mechanical brake (EMB) employing an electric motor, in the place of an existing hydraulic brake, to brake wheels has emerged, for which, thus, various EMB products have been developed.
Referring to a structure of an EMB product, it has a mechanism, eliminating a hydraulic driving unit (hydraulic cylinder or piston) for pressing pads in an existing hydraulic disk brake, a motor driving unit (a motor, a roller screw, a decelerator, etc.) is used instead and a rotary disk is braked by using a motor as a power source.
This mechanism is similar to that of a floating caliper type of a hydraulic disk brake.
Namely, using a motor as a power source, an inner pad is first moved and clamped, and a sliding caliper is moved by reaction force since then, to clamp an outer pad, thus performing braking.
Thus, the related art EMB product still involves the generation of wear variations between the inner pad and the outer pad, namely, the shortcomings of the floating caliper type remain unsolved, and due to the operational principle (after the inner pad is moved and clamped, the caliper is moved by reaction force to clamp the outer pad), it takes more time to reach required braking force, compared with a fixed type, degrading responsiveness.